Keep your friends close, and your enemies closer. The metalmark butterfly cooperates with ants when it’s a caterpillar, only to stab them in the back when it has metamorphosed into a beautiful – thieving – butterfly.

While still a caterpillar, the metalmark butterfly wins over local ants, including those of the species Ectatomma tuberculatum, with gifts of sugary secretions (see gif below). In return, the ants, which could easily eat the caterpillar or its adult butterfly form, defend the vulnerable caterpillars from other predators.

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But this friendly give-and-take doesn’t last forever, work by Phillip Torres of Rice University in Houston, Texas and Aaron Pomerantz of the University of Florida, Gainesville, has now revealed. When the caterpillars have become butterflies, they turn on their protectors, plundering the source of their nectar.

Ants taking secretions from caterpillars

@AaronPomerantz

This nectar is produced by organs called nectaries at the tips of new bamboo shoots, which are tended by ants. Using their mouthparts, they improve the flow from these nectaries, and stop them from running dry. The nectar is an important source of food for them, so they defend these nectaries fiercely.

Pleasing perfume

Once mature, the butterflies start helping themselves to the ants’ sugary food source, drinking directly from the nectaries in plain sight of the ants. After a few attempts to stop this, the ants give up and wait their turn.

Allowing the butterflies to feed for free is unlikely to be a beneficial move on the ants’ part. Bamboo grows very quickly, and the butterflies only lay their eggs on young shoots. When the adults are ready to breed, they fly away and lay their eggs elsewhere, meaning that the ants are unlikely to benefit from a relationship with the thieving adults’ offspring.

Torres thinks the butterflies get away with this thanks to a particular perfume. If the butterflies still smell the same as the caterpillars, this may trigger the ants to continue protecting them, in the expectation of more sugary secretion gifts.

Butterfly drinking from an ant’s mouth

@phil_torres

Torres has observed some species of ant using their antennae to drum the backs of the butterflies’ bodies . This is the same behaviour they use to stimulate caterpillars to give them a sugary present.

But these ants leave empty handed – the butterflies never pay out, despite drinking from the nectar larder for hours.

To add insult to injury, the butterflies disguise themselves as ants to evade other predators. Ant-like patterns on their wings are thought to trick animals like birds that might otherwise snatch a butterfly while it was drinking nectar. “Ants don’t taste good and they have chemical defences,” says Torres.